Baby keeps falling and getting stuck on her bakc.

One of my 3 day old Silkies keeps falling (tripping over another chick, or toppling over when she is reaching behind her to scratch), and she keeps getting stuck on her back and just flails. Three times the past 6 or 7 hours I've found her flailing and had to help right her. I'm afraid she'll get stuck when I'm not around and die. Why is this happening? They are in a cardboard box lined with paper towels right now. Would it help to go ahead and put them on pine shavings? I'm so worried for this little girl. She SEEMS healthy and is eating/drinking/pooping, but she just keeps getting stuck.